Method and apparatus for reconstructing missing color samples

ABSTRACT

Apparatus and method for sensing sampled colored image data and thereafter interpolating the sampled colored image data to provide image data in each color sampled for each point or pixel at which the subject is sensed from which an image of the subject may be constructed having reduced color artifacts and fringing while reducing the blurring to the image that would otherwise be required to correct for such artifacts and fringing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to an apparatus and method for sensingand interpolating image data and, more particularly, to an apparatus andmethod for sensing sampled image data and thereafter interpolating forthe nonsampled image data in a manner that substantially reduces colorfringing.

2. Description of the Prior Art

Electronic imaging cameras for recording still images are well known inthe art. Such cameras can record a plurality of still images on a singlemagnetic disk or tape in either analog or digital format for subsequentplayback on any well-known cathode ray tube viewing device. Printers mayalso be utilized with such cameras in a well-known manner to providehard copy of the recorded images. Such electronic imaging still camerasmay utilize two-dimensional image sensing arrays such as charge coupleddevices (CCD's) which integrate incident scene light over apredetermined time to provide an electronic information signalcorresponding to the scene light intensity incident to the array. Suchtwo-dimensional image sensing arrays comprise a predetermined number ofdiscrete image sensing elements or pixels arranged in a two-dimensionalarray in which each image sensing element responds to incidentillumination to provide an electronic information signal correspondingto the intensity of the incident illumination.

In order to record color images the incident illumination to thetwo-dimensional image sensing array is filtered so that different imagesensing elements received different colored illumination. The filtersare arranged in well-known patterns across the face of the image sensingarray such as a repeating pattern of red, green and blue stripes.Alternatively, individual image sensing elements or pixels across eachline may be filtered in a repeating pattern of red, green, blue, greenfilters, as is well known in the art. Since each image sensing elementcan only detect one color of illumination, the color information for theother colors not detected by that image sensing element must be filledin. Filling in the missing color information is generally accomplishedby interpolating the detected image data for each color to determinecolor values for all the colors for each image sensing element.

Conventional types of interpolation, however, can provide images withobjectionable aliasing artifacts such as "color fringes" near sharpedges. The conventional approach to solve this problem is to eliminatethe color fringes at the expense of image sharpness by blurring(antialiasing) the picture so that the edges are not sharp enough tocreate a color fringe. Blurring the image in this manner, however, hasits obvious disadvantages resulting in a reduction in resolution and aso-called "fuzzy" picture.

Therefore, it is a primary object of this invention to provide anelectronic imaging camera which interpolates sampled color image data ina manner that substantially reduces color fringing without the amount ofblurring (antialiasing) otherwise required.

It is an even further object of this invention to provide an electronicimaging camera in which sampled image data is interpolated to provideimage data in all the colors for all the image sensing elements whileminimizing color artifacts without the amount of blurring (antialiasing)otherwise required.

Other objects of the invention will be in part obvious and will in partappear hereinafter. The invention accordingly comprises a mechanism andsystem possessing the construction, combination of elements andarrangement of parts which are exemplified in the following detaileddisclosure.

SUMMARY OF THE INVENTION

An electronic imaging camera comprises an image sensing array having apredetermined number of discrete image sensing elements each of whichresponds to incident illumination from a subject to provide anelectronic information signal corresponding to the intensity of theillumination incident thereto. Means are provided for filtering theillumination incident to the image sensing array so that at least afirst group of image sensing elements receives illumination within afirst select range of wavelengths and a second group of image sensingelements receives illumination within a second select range ofwavelengths different from the first select range. Means are providedfor interpolating the electronic information signals from the firstgroup of image sensing elements to provide a first set of electronicinformation signals corresponding to the intensity of illuminationwithin the first range of wavelengths for both the first and secondgroups of image sensing elements and for interpolating electronicinformation signals from the second group of image sensing elements toprovide a second set of electronic information signals corresponding tothe intensity of illumination within the second range of wavelengths forboth the first and second groups of image sensing elements. Means areprovided for combining the first and second sets of electronicinformation signals from the interpolating means and thereaftermodifying the combined electronic information signals by replacing thecombined electronic information signal corresponding to each imagesensing element with a median value of the combined electronicinformation signals corresponding to a select number of image sensingelements in the vicinity thereof to provide a median electronicinformation signal for each image sensing element. Means are providedfor thereafter combining the median electronic information signal foreach image sensing element in the first group of image sensing elementswith the electronic information signal originally sensed for that sameimage sensing element in the first group to provide an output electronicinformation signal corresponding to the intensity of illumination withinthe second range of wavelengths for each of the first group of imagesensing elements. Means are provided for also combining the medianelectronic information signal for each image sensing element in thesecond group of image sensing elements with the electronic informationsignal originally sensed for that same image sensing element in thesecond group to provide an output electronic information signalcorresponding to the intensity of incident illumination within the firstrange of wavelengths for each of the second group of image sensingelements.

DESCRIPTION OF THE DRAWINGS

The novel features that are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with other objects and advantages thereof will bebest understood from the following description of the illustratedembodiment when read in connection with accompanying drawings wherein:

FIG. 1 is a graphical representation of an example of the distributionof light intensity incident to an image sensing array;

FIG. 2 is a graphical representation of the illumination incident to theimage sensing array of FIG. 1 having a filter arrangement in whichalternate image sensing elements are overlapped by different coloredfilters;

FIG. 3 is a graphical representation of the distribution of linearlyinterpolated color light intensity values for the image sensing elementsof the image sensing array of FIG. 1;

FIG. 4 is a graphical representation showing the difference between thetwo color light intensity values for each image sensing element of theimage sensing array of FIG. 1;

FIG. 5 is a graphical representation of the color light intensity valuesof FIG. 4 subsequent to median filtering;

FIG. 6 is a graphical representation of the color light intensity valuesof both colors detected by the image sensing array of FIG. 1interpolated in the manner of this invention;

FIG. 7 is a schematic block diagram for an electronic imaging camerawhich interpolates image data in the manner of this invention;

FIG. 8 is a schematic circuit diagram for the median filter of FIG. 7;

FIG. 9 is a schematic block diagram for an alternate embodiment to theelectronic imaging camera of FIG. 7; and

FIGS. 10A-C are a graphical representations for different voltagewaveforms at different nodes of the circuit of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As previously discussed, electronic imaging cameras conventionallyrecord color images by using an image sensing array comprising apredetermined number of discrete image sensing elements or pixelsarranged in a two-dimensional array in which the image sensing elementsrespond to incident illumination to provide an electronic informationsignal corresponding to the intensity of the incident illumination. Suchimage sensing arrays may be a charge coupled device (CCD) of the frametransfer type. It is well known to sense color images using a singletwo-dimensional CCD array by filtering the illumination incident to theimage sensing array so that different groups of the image sensingelements arranged in well-known patterns across the image sensing arrayreceive different wavelength or colored illumination. Thus, each colorof illumination is sampled by each group of image sensing elements andthereafter interpolated to provide color values corresponding to theother groups of image sensing elements. The full color image istherefore estimated or interpolated between the different groups ofimage sensing elements or pixels to fill in all the colors for eachimage sensing element or pixel.

Conventional types of interpolation provide images with objectionablealiasing artifacts such as color fringes near sharp edges. As previouslydiscussed, the conventional solution to this problem is to eliminate thecolor fringes at the expense of image sharpness by blurring(antialiasing) the reproduced image so that the edges are not sharpenough to create a color fringe. An example of how a sharp edge in asubject to be recorded can create color fringes when the image of thesubject is reconstructed using conventional interpolation methods willnow be discussed. Referring now to FIG. 1, there is shown a graphicalrepresentation of the light intensity distribution incident to an imagesensing CCD array comprising, for example, 17 individual image sensingelements or pixels. For simplicity it will be assumed that theillumination comprises two colors A and B wherein each color is definedby a select range of wavelengths different from the select range ofwavelengths which defines the other color. As is readily apparent fromthe graph of FIG. 1, the incident illumination defines a sharp grey edgebetween the pixels 6 and 7 and a sharp grey to color transition betweenpixels 12 and 13.

Referring now to FIG. 2, there is shown a graphical representation ofthe illumination incident to an image sensing CCD array having a filterarrangement in which alternate image sensing elements or pixels areoverlapped by filters transmitting either color A or color B. Thus, eachimage sensing element or pixel receives a single color of illumination,and linear interpolation between the image sensing elements or pixelswhich sample each color provides the color distribution as showngraphically in FIG. 3. As is now readily apparent, the image sensingelements or pixels 6 and 7 on each side of the grey edge no longerprovide equal intensities for the colors A and B and thus will provide ahighly visible color artifact or fringe in the reconstructed image.

Referring now to FIG. 7 there is shown a schematic diagram for anelectronic imaging camera 10 which interpolates image data in the mannerof this invention so as to avoid creating the aforementioned colorfringes. The electronic imaging camera 10 comprises an objective lens 12for directing scene light by way of a shutter 14 to an image sensingarray 16. The shutter 14 is controlled in a conventional manner by meansnot shown. The image sensing array 16 comprises a predetermined numberof discrete image sensing elements or pixels arranged in atwo-dimensional array in which the image sensing elements respond toincident illumination to provide an electronic information signalcorresponding to the intensity of the incident illumination. Aspreviously discussed, the image sensing array may comprise a chargecoupled device (CCD) of the frame transfer type.

The electronic information signal output corresponding to the color A isdirected to a conventional linear interpolator 18 which interpolates thesampled A color information to provide an electronic information signalfor each image sensing element or pixel corresponding to the color A asshown in FIG. 3. In like manner, the electronic information signalscorresponding to the color B are directed to a linear interpolator 18'in which the sampled B color information is interpolated to provide anelectronic information signal for each image sensing element or pixelcorresponding to the color B as also shown in FIG. 3.

The output electronic information signals from the linear interpolators18 and 18', in turn, are directed to a subtractor 22 which operates tosubtract the electronic information signals corresponding to color Bfrom the electronic information signals corresponding to color A toprovide an output which is shown graphically in FIG. 4. The graph ofFIG. 4 shows that the difference between the colors A and B rapidlyincreases and then decreases in the area of the sharp grey edge betweenpixels 6 and 7. It is this rapid increase and decrease in the differencebetween the two colors which is characteristic of the objectionablecolor fringing and not simply a sudden rise in the difference betweencolors A and B as occurs after pixel 11 and which is indicative of achange from one color to a different color. Thus, it is unlikely that areal scene would result in the creation of such a color spike at thepixels 6 and 7, and it is not desirable to create such a color spike asa result of the method of interpolation chosen.

A better estimate of the actual difference between the values for thecolors A and B is provided by the graphical representation of FIG. 5where the sharp peaks and valleys are removed and the other sharptransitions retained. Toward this end there is provided a median filter24 which replaces the value as shown graphically in FIG. 4 for eachimage sensing element or pixel with the median value of a predeterminednumber of neighboring image sensing elements or pixels. Thus, the medianfilter 24 has a width of N image sensing elements or pixels and operatesto replace each value in the graph of FIG. 4 with the median value ofthe nearest N image sensing elements or pixels. For example, if thewidth of the median filter 24 is selected to be five image sensingelements or pixels, then the value at pixel 6 will become the medianvalue of the pixels 4, 5, 6, 7 and 8. When the values for the pixels 4,5, 6, 7 and 8 are sorted into descending order and counted down threefrom the top, it becomes readily apparent that the median value for thepixel 6 is 0 and thus the median filter 24 operates to substitute thevalue 0 `for the pixel 6. Although the median filter 24 operates toremove sharp spikes and valleys, it will leave sharp monotonicallyincreasing or decreasing edges intact as occurs between pixels 11 and 13in FIG. 4. Thus, the electronic information output signal from themedian filter 24 is shown graphically in FIG. 5 with the sharp spike atpixels 6 and 7 removed and the increasing edge of pixels 11 and 13intact. Although a median filter is described for the preferredembodiment, the invention is by no means so limited and other types offilters such as other nonlinear filters or low pass, high pass filters,etc. could alternatively be utilized.

Since the median values for each pixel are derived from the values ofcolor A minus the values of color B for each pixel, directing the medianvalues to a subtractor 26 for subtraction from the values for the colorA operates to provide the values for the color B for those image sensingelements or pixels that receive only A colored light. In like manner,the median output values from the median filter 24 are directed to anadder 28 for addition to the values for the color B to provide the Acolored light values for those picture sensing elements or pixels thatreceive only B colored light. In this manner there is provided aninterpolated value for the B colored light for each picture sensingelement or pixel that senses only the A colored light and, conversely,an interpolated value for the A colored light is provided for eachpicture sensing element or pixel that senses only the B colored light asbest shown by the graphical representation of FIG. 6. As is now readilyapparent, the interpolation technique of this invention operates toactively reconstruct the sharp grey edge between the pixels 6 and 7while maintaining the color divergence starting at the pixel 11.

Referring now to FIG. 8 there is shown a circuit diagram for the medianfilter 24 comprising a tapped delay line 36 connected to receive theinput signal from the subtractor 22. Each output line from the tappeddelay line 36, in turn, connects to a respective input line of aplurality of comparators 38A through 38E. The other input terminals tothe comparators 38A through 38E, in turn, are in common connection withrespect to each other and receive a varying voltage 48 also shown inFIG. 10A which varies over the range in which the electronic informationsignals from the image sensing elements or pixels varies. The outputsignals from the comparators 38A through 38E, in turn, are directed forsummation by an adder 39 which, in turn, provides an output signal toanother comparator 40. The other input terminal to the comparator 40 isconnected to a predetermined reference voltage, and the output terminalfrom the comparator 40 is directed to a tristate buffer 42. The outputfrom the tristate buffer 42, in turn, operates to control a sample andhold circuit 44 which samples the value of the varying voltage 48 andupon the actuation thereof holds the value of the voltage 48 at outputterminal 46. A pull-up resistor 47 connected between the output from thetristate buffer 42 and a supply voltage V₀ operates to provide anaffirmative enabling signal to the sample and hold circuit 44 when thetri-state buffer is disabled in a manner as will be subsequentlydescribed.

During operation, the voltage values corresponding to a plurality ofadjacent picture sensing elements or pixels are serially directed to thetapped delay line 36 so as to connect the input to each one of thecomparators 38A through 38E to a value corresponding to a respective oneof the selected number of picture sensing elements or pixels chosen todefine the median filter width. As the voltage level 48 at the inputnode gradually increases, comparators 38A through 38E switch to providehigh (binary logic 1) affirmative enabling signals which when addedtogether by the adder 30 operate to switch the comparator 40 at themedian filter value.

For example, in the illustrated embodiment of FIG. 8 there are providedfive comparators 38A through 38E which may each provide a 5 voltaffirmative (binary logic 1) output voltage upon being switched. Thus,as is now readily apparent, an output from the adder 39 of 15 voltsoccurs when the median comparator of the comparators 38A through 38Eswitches as a function of the gradually increasing voltage 48. The 15volt output from the adder 39, in turn, operates to switch thecomparator 40 which provides an affirmative output signal to the inputof the tristate buffer 42.

The tristate buffer 42 is controlled by a timing signal as shown in FIG.10B from a timing control circuit 49 so as to be enabled when thevarying voltage 48 increases and disabled when the varying voltage 48decreases as best shown in FIGS. 10A and 10B. Before the comparator 40provides its affirmative output signal, the controlling signal to thesample and hold circuit 44 is held low by the output of the comparator40. The sample and hold circuit 44 therefore samples the graduallyincreasing voltage 48; and, when the comparator 40 provides itsaffirmative output signal, that signal passes through the tristatebuffer 42 since it is enabled and causes the sample and hold circuit 44to hold the voltage value sampled at that instant from the varyingvoltage 48 at the output terminal 46. In this manner there is providedthe median output voltage corresponding to each picture sensing elementor pixel as determined from the values corresponding to at least fourmore adjacent picture sensing elements or pixels as shown in FIG. 10C.As is readily apparent, the number of comparators 38A through 38E may beincreased or decreased to vary the number of picture sensing elements orpixels from which each median value is determined.

After the varying voltage 48 reaches its peak and begins to decrease,the output of the tristate buffer 42 is disabled by the timing signal asshown in FIG. 10B from the timing control 49, and the input signal levelto sample and hold circuit 44 is held high by the pull-up resistor 47causing the sample and hold circuit 44 to continue to hold the medianvoltage level until varying voltage 48 begins to rise again and themedian value of the next group of pixels is about to be determined. Itis readily apparent that the output 46 could be the input to a secondsample and hold circuit (not shown) which could sample the output signalduring the descending portion of the varying voltage 48 and hold thesampled median voltage during the rising part of the next succeedingcycle of the varying voltage 48. Thus, the output signal at all timeswould represent a median output value.

The two color system of FIG. 7 may be expanded to a three color systemas shown in FIG. 9 where like numerals designate previously describedelements. The image sensor 16 provides output electronic informationsignals corresponding to three different colors or wavelengths ofincident illumination A, B and C which may, for example, be red, greenand blue. Electronic information signals A derived from sensing the Acolored illumination are directed to the linear interpolator 18 forinterpolating values for the A colored illumination for those imagesensing elements or pixels which are filtered to receive the B coloredillumination and the C colored illumination. In like manner, theelectronic information signals B derived from sensing the B coloredillumination are directed to the linear interpolator 18' to interpolatethose values for the B colored illumination corresponding to the imagesensing elements or pixels which are filtered to receive the A and Ccolored illumination. Again, in like manner, the electronic informationsignals C derived from sensing the C colored illumination are directedto the linear interpolator 18" to interpolate the values for the Ccolored illumination corresponding to the image sensing elements orpixels which are filtered to receive the A and B colored illumination.

The subtractor 22 operates in the aforementioned manner to provide avalue corresponding to the difference between the A and B coloredillumination for each light sensing element or pixel which output isthereafter directed to the median filter 24 for filtering in theaforementioned manner. The electronic information output signals fromthe median filter 24 are thereafter subtracted from the output valuessensed for the A colored illumination by the subtractor 26 to providevalues B₁ corresponding to the B colored illumination for each imagesensing element or pixel that is filtered to receive the A coloredillumination. The electronic information output signals from the medianfilter 24 are also added to the output values sensed for the B coloredillumination by the adder 28 to provide values A₂ corresponding to the Acolored illumination for each image sensing element or pixel that isfiltered to receive the B colored illumination. The subscript 1 denotesvalues for the A, B and C colored illumination for those image sensingelements or pixels which are filtered to receive the A coloredillumination. In like manner, the subscript 2 denotes values for the A,B and C colored illumination for those image sensing elements or pixelsthat are filtered to receive the B colored illumination while thesubscript 3 denotes values for the A, B and C colored illumination forthose image sensing elements or pixels which are filtered to receive theC colored illumination.

The linear interpolator 18" operates in the aforementioned manner toprovide output values for the C colored illumination corresponding tothose image sensing elements or pixels which are filtered to receive theA and B colored illumination. The output from the linear interpolator18" is subtracted from the output from the linear interpolator 18' andthereafter median filtered by the median filter 24' to provide medianvalues which are thereafter combined by the adder 28' with the valuessensed for the C colored illumination to provide output values B₃ forthe B colored illumination corresponding to those light sensing elementsor pixels filtered to receive the C colored illumination. In likemanner, the output from the median filter 24' is also combined by thesubtractor 26' with the output values sensed for the B coloredillumination to provide output values C₂ corresponding to the C coloredillumination for those image sensing elements or pixels filtered toreceive the B colored illumination.

The output from the linear interpolator 18" is also directed to anothersubtractor 22" for subtraction from the A colored values interpolated bythe linear interpolator 18. The output from the subtractor 22" , inturn, is directed to the median filter 24" to provide an output in theaforementioned manner which is subsequently subtracted from the valuessensed for the A colored illumination by a subtractor 26" to provide theoutput values C₁ corresponding to the C colored illumination for thoseimage sensing elements or pixels filtered to receive the A coloredillumination. In like manner, the output from the median filter 24" isdirected to another adder 28" for addition to the output values sensedfor the C colored illumination to provide output values A₃ correspondingto the A colored illumination for those light sensing elements or pixelsfiltered to receive the C colored illumination. Thus, in this mannerthere is provided an interpolated value for each of the three colors A,B and C for each image sensing element or pixel.

The aforementioned invention is also applicable to linear light sensingarrays, and the illustrated embodiment could alternatively comprise theprocessing of a single line of a linear light sensing array.

Other embodiments of the invention, including additions, subtractions,deletions and other modifications of the preferred disclosed embodimentsof the invention will be obvious to those skilled in the art and arewithin the scope of the following claims.

What is claimed is:
 1. An electronic imaging camera comprising:an image sensing array comprising a predetermined number of discrete image sensing elements each of which is responsive to incident illumination from a subject to provide an electronic information signal corresponding to the intensity of the illumination incident thereto; means for filtering the illumination incident to said image sensing array so that at least a first group of said image sensing elements receives illumination within a first select range of wavelengths and a second group of said image sensing elements receives illumination within a second select range of wavelengths different from said first select range; means for interpolating the electronic information signals from said first group of image sensing elements for providing a first set of electronic information signals corresponding to the intensity of illumination within said first range of wavelengths for both said first and second groups of image sensing elements and for interpolating the electronic information signals from said second group of image sensing elements for providing a second set of electronic information signals corresponding to the intensity of illumination within said second range of wavelengths for both said first and second groups of image sensing elements; means for combining said first and second sets of electronic information signals from said interpolating means and thereafter modifying said combined electronic information signals by replacing the combined electronic information signal corresponding to each image sensing element with a filtered value of the combined electronic information signals to provide a filtered electronic information signal for each image sensing element; and means for combining said filtered electronic information signal for each image sensing element in said first group of image sensing elements with the electronic information signal originally sensed for that same image sensing element in said first group to provide an output electronic information signal corresponding to the intensity of incident illumination within said second range of wavelengths for each of said first group of image sensing elements, and for combining said filtered electronic information signal for each image sensing element in said second group of image sensing elements with the electronic information signal originally sensed for that same image sensing element in said second group to provide an output electronic information signal corresponding to the intensity of incident illumination within said first range of wavelengths for each of said second group of image sensing elements.
 2. The electronic camera of claim 1 wherein said filtered value of the combined electronic information signal for each image sensing element comprises the median value of the combined electronic information signals for a select number of image sensing elements in the vicinity thereof.
 3. The electronic camera of claim 2 wherein said means for interpolating operates to linearly interpolate.
 4. The electronic camera of claim 2 wherein said means for combining said first and second sets of electronic information signals from said interpolating means operates to subtract said second set of electronic information signals from said first set of electronic information signals to provide said combined electronic information signals.
 5. The electronic camera of claim 2 wherein: said means for filtering the illumination incident to said image sensing array operates so that a third group of image sensing elements receives illumination within a third select range of wavelengths, said interpolating means operates to: interpolate the electronic information signals from said first group of image sensing elements to provide a first set of electronic information signals corresponding to the intensity of illumination within said first range of wavelengths for said first, second and third groups of image sensing elements, interpolate the electronic information signals from said second group of image sensing elements to provide a second set of electronic information signals corresponding to the intensity of illumination within said second range of wavelengths for said first, second and third groups of image sensing elements, and interpolate the electronic information signals from said third group of image sensing elements to provide a third set of electronic information signals corresponding to the intensity of illumination within said third range of wavelengths for said first, second and third groups of image sensing elements; wherein said means for combining said sets of electronic information signals operates to combine said first and second sets of electronic information signals, said second and third sets of electronic information signals, and said first and third sets of electronic information signals, said combined electronic information signals being thereafter modified by replacing the electronic information signal corresponding to each image sensing element with the median value of the electronic information signals corresponding to a select number of image sensing elements in the vicinity thereof to provide a median electronic information signal for each image sensing element; and said median electronic information signal combining means operates to: combine said median electronic information signal for each image sensing area in said first group of image sensing elements with the electronic information signal originally sensed for that same image sensing element in said first group to provide an output electronic information signal corresponding to the intensity of incident illumination within said second and third ranges of wavelengths for each of said first group of image sensing elements, combine said median electronic information signal for each image sensing element in said second group of image sensing elements with the electronic information signal originally sensed for that same image sensing element in said second group to provide an output electronic information signal corresponding to the intensity of incident illumination within said first and third ranges of wavelengths for each of said second group of image sensing elements, and combine said median electronic information signal for each image sensing element in said third group of image sensing elements with the electronic information signal originally sensed for that same image sensing element in said third group to provide an output electronic information signal corresponding to the intensity of incident illumination within said first and second ranges of wavelengths for each said third group of image sensing elements.
 6. The electronic camera of claim 5 wherein said means for combining said first and second sets of electronic information signals operates to subtract said second set of electronic information signals from said first set of electronic information signals, said means for combining said second and third sets of electronic information signals operates to subtract said third set of electronic information signals from said second set of electronic information signals, and said means for combining said first and third sets of electronic information signals, operates to subtract said third set of electronic information signals from said first set of electronic information signals.
 7. The electronic camera of claim 2 wherein said means for modifying said combined electronic information signals to provide a median electronic information signal comprises a delay line having a plurality of tapped output terminals therefrom, a plurality of comparators each having one input terminal connected to a respective one of said plurality of tapped output terminals and the other input terminal connected to receive a source of varying voltage, means for combining the output signals from said plurality of comparators to provide a combined output signal, means for comparing said combined output signal with a select reference voltage level and for providing an affirmative output voltage level upon said combined output signal equaling said select reference voltage level; and means for sampling and holding the voltage level of the source of varying voltage responsive to said affirmative output voltage.
 8. The electronic camera of claim 6 including a tristate buffer circuit responsive to said affirmative output voltage for actuating said means for sampling and holding to sample and hold the voltage level of the source of varying voltage, means for timing the enablement and disablement of said tristate buffer circuit in order to provide median electronic information signals for succeeding image sensing elements, and resistor means for maintaining said affirmative output voltage upon the disablement of said means for sampling and holding by said timing means.
 9. A method of sensing a subject and providing an output from which a visible image of the subject may be constructed comprising the steps of:sensing light from the subject with an image sensing array comprising a predetermined number of discrete image sensing elements each of which responds to incident illumination from the subject to provide an output corresponding to the intensity of the illumination incident thereto; filtering the illumination incident to the image sensing array so that at least a first group of image sensing elements receives illumination within a first select range of wavelengths and a second group of image sensing elements receives illumination within a second select range of wavelengths different from the first select range; interpolating the outputs from the first group of image sensing elements to provide a first set of outputs corresponding to the intensity of illumination within the first range of wavelengths for both said first and second groups of image sensing elements; interpolating the outputs from the second group of image sensing elements to provide a second set of outputs corresponding to the intensity of illumination within the second range of wavelengths for both the first and second groups of image sensing elements; combining the first and second sets of outputs and thereafter modifying the combined outputs by replacing the combined output corresponding to each image sensing element with a filtered value of the combined outputs to provide a filtered output for each image sensing element; and combining said filtered output for each image sensing element in the first group of image sensing elements with the output originally sensed for that same image sensing element in the first group to provide an output corresponding to the intensity of incident illumination within the second range of wavelengths for each of the first group of image sensing elements and combining the filtered output for each image sensing element in the second group of image sensing elements with the output originally sensed for that same image sensing element in the second group to provide an output corresponding to the intensity of incident illumination within the first range of wavelengths for each of the second group of image sensing elements.
 10. The method of claim 9 wherein said step for providing a filtered output for each image sensing element provides the median value of the combined electronic information signals for a select number of image sensing elements in the vicinity thereof.
 11. The method of claim 10 wherein said step of interpolating is a linear interpolation.
 12. The method of claim 10 said step of combining the first and second sets of outputs subsequent to interpolation comprises the step of subtracting the second set of outputs from the first set of outputs to provide the combined output.
 13. The method of claim 10 wherein: said step of filtering the illumination incident to the image sensing array further includes filtering the illumination so that a third group of image sensing elements receives illumination within a third select range of wavelengths; said step of interpolating further includes: interpolating the outputs from the first group of image sensing elements to provide a first set of outputs corresponding to the intensity of illumination within the first range of wavelengths for the first, second and third groups of image sensing elements, interpolating the outputs from the second group of image sensing elements to provide a second set of outputs corresponding to the intensity of illumination within the second range of wavelengths for the first, second and third groups of image sensing elements, and interpolating the outputs from the third group of image sensing elements to provide a third set of outputs corresponding to the intensity of illumination within the third range of wavelengths for the first, second and third groups of image sensing elements; said step of combining the sets of outputs further operates to combine the first and second sets of outputs, the second and third sets of outputs, and the first and third sets of outputs, said step of modifying thereafter replacing the output corresponding to each image sensing element with the median value of the output corresponding to a select number of image sensing elements in the vicinity thereof to provide a median output for each image sensing element; said step of combining the median outputs further combining: the median output for each image sensing element in the first group of image sensing elements with the output originally sensed for that same image sensing element in said first group to provide an output corresponding to the intensity of incident illumination within the second and third range of wavelengths for each of the first group of image sensing elements, the median output for each image sensing element in the second group of image sensing elements with the output originally sensed for that same image sensing element in said second group to provide an output corresponding to the intensity of incident illumination within the first and third range of wavelengths for each of the second group of image sensing elements, and the median outputs for each image sensing element in the third group of image sensing elements with the output originally sensed for that same image sensing element in said third group to provide an output corresponding to the intensity of incident illumination within the first and second range of wavelengths for each of the third group of image sensing elements.
 14. The method of claim 13 wherein said step of combining said first and second sets of outputs operates to subtract said second set of outputs from said first set of outputs, said step of combining said second and third sets of outputs operates to subtract said third set of outputs from said second set of outputs, and said step of combining said first and third sets of outputs operates to subtract said third set of outputs from said first set of outputs. 